1. Field
The embodiments discussed herein are directed to a data transmission circuit and its control method.
2. Description of the Related Art
The Japanese Patent Laid-Open No. 2000-180481 discloses the technology of a multi-carrier modulation system for detecting a received signal (tone signal) of a single frequency signal. The technology of the Japanese Patent Laid-Open No. 2000-180481 refers to a single frequency signal detection apparatus for detecting each frequency of a received signal having a different frequency, and the apparatus includes level detection means for comparing a received signal with a threshold and detecting a level; pulse width measurement means for measuring a pulse width in detecting the level by the level detection means; clock/count means for counting the number of pulses corresponding to the pulse width measured by the pulse width measurement means; and frequency identification means for outputting a detection signal indicating a single frequency signal in a received signal from the number of pulses counted by the clock/count means.
In the technology of the Japanese Patent Laid-Open No. 2000-180481, the pulse width measurement means performs a masking process of not counting a pulse having a width shorter than the pulse set as a result of measuring a pulse width by the level detection means.
According to the technology of the Japanese Patent Laid-Open No. 2000-180481, a short pulse generated by noise is masked and not counted. Therefore, a tone signal can be surely detected from a received signal superposed by noise, thereby acquiring good detection features.
In addition, according to the technology of the Japanese Patent Laid-Open No. 2000-180481, only a comparator is designed to operate during standby, and the power consumption during standby can be reduced.
Meanwhile, in a recent vehicle-installed communication network, a tone signal is transmitted using the IEEE1394 standard with a plastic optical fiber (POF).
In addition, in a recent vehicle-installed communication control LSI, there is an increasing demand for reducing power consumption. Therefore, in the above-mentioned vehicle-installed communication control LSI, to reduce the power consumption during standby when an engine stops, for example, the current consumption of a reception unit of a tone signal transmitted by a POF is suppressed to be 20 μA or less.
However, while the data transmission rate of the POF is 200 Mbps, the data transmission rate of a copper wire is 400 Mbps. Therefore, it is desired to form a transmission line of a tone signal and a data signal through the copper wire to transmit a data signal at a higher speed while reducing the power consumption like the IEEE1394 standard using the POF.
On the other hand, as compared with the POF, a copper wire is subject to the effect of noise. Therefore, when a transmission line, such as the tone signal etc., is formed by a copper wire, it is considered that a reception unit of the vehicle-installed communication control LSI more easily receives a noise signal than when a transmission line of the tone signal etc. is formed by the POF. Therefore, the vehicle-installed communication control LSI erroneously recognizes that a tone signal has been received although the reception unit has actually received a noise signal. As a result, there is the possibility that a malfunction of transmitting a wakeup signal occurs in peripheral equipment coupled to the vehicle-installed communication control LSI.